The present disclosure is directed to a variable cycle intake for a propulsion system having a reverse core engine, which variable cycle intake has a first position for supplying free stream air to an inlet of the engine and a second position for supplying fan stream air to the inlet of the engine.
Typical multi-spool turbofan engines include a nested core, in which a high pressure, or core, spool is nested inside a low pressure spool. Such a nested core engine includes, in axial sequence, a low pressure compressor, a high pressure compressor, a combustor section, a high pressure turbine, and a low pressure turbine. The high pressure compressor is connected to the high pressure turbine with a high pressure shaft that extends through the combustor section. The low pressure compressor is connected to the low pressure turbine with a low pressure shaft that extends through the high pressure shaft. Increases in efficiency of the turbofan allow for the core to be reduced in size, such as by having a smaller diameter. The low pressure shaft, however, cannot be reduced in diameter because the rotational speeds of the low pressure spool are limited by critical speed. The shaft critical speed is proportional to the shaft diameter and inversely proportional to the shaft length. Thus, decreasing the shaft diameter with reduced core sizes is not possible without reducing the shaft length if the same critical speed is desired. Thus, reductions in the core size yields compromises in the high pressure spool to accommodate low pressure spool shaft diameters. For example, the size and weight of high pressure spool rotor disk need to be increased to accommodate openings for larger low pressure shaft sizes. As such, there is a need for improving engine architectures to allow for, among other things, decreased core sizes resulting from more efficient turbofan engines.
There has been proposed a gas turbine engine comprising a fan drive gear system, a low spool connected to the fan drive gear system, and a high spool disposed aft of the low spool. The low spool comprises a rearward-flow low pressure compressor disposed aft of the fan drive gear systems, and a forward flow low pressure turbine disposed aft of the low pressure compressor. The high spool comprises a forward flow high pressure turbine disposed aft of the low pressure turbine, a combustor disposed of aft of the high pressure turbine, and a forward-flow high pressure compressor disposed aft of the combustor.
One issue faced by designers of these new engine architectures is incorporation of the new engine architecture into an aircraft.